Tom, by 'open' do you mean you have non-limited slip (non-positraction)? And by 'four spider gears', are two splined for your axles and two are on the carrier pin? I guess I'm asking if this is a regular conventional setup or something that is custom.

The only reason we use low ratios (like 3.9:1 or 4.30:1) is for launches. Tall gears (like 2.75) tend to come apart when 400-500 HP tries to spin slicks off the line. I've seen axles twisted a half-turn as a result as well.

A 4.30 ratio will easily transfer 500 HP because more ring and pinion gear teeth are engaged at once and torque is doubled over a 2.75 just because of the ratio. I've seen 'tall' gears explode upon launch.

Bonneville cars use tall gears because they are looking for 'maximum top end speed' regardless of how long it takes to get there.

I don't know why but Ford puts tall gears in convertibles. When my Mustang was stock, the 5.0/AOD got me to 150 MPH but it took a very long time to get there and there was more elbow room left on the tach. The engine simply didn't have any more to give. Not bad for 'stock' but I wasn't satisfied with acceleration so I built a 351W. - Dave

Good comments Dave.

And yes Dave, it's a non-posi rear end, it has four spider gears, two on the normal pin that goes through the carrier and the other two on short pins that go into the centre 'block that the long pin passes through.

When one wheel is spinning it shares the load on the side gears with four gears instead of two.

And I've seen teeth shred off a real low geared set (5:13 etc) pinion because of the small diameter of the pinion so there's give and take I guess!.

But I like my 2:75 gears as it gives a semblance of 'economy' (huh!) and I have never run out of revs in top gear.

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